Field of the Invention
The present invention relates to an electrical machine comprising:
a rotor configured to rotate in a direction relative to a stator, where the rotor comprises one or more poles configured to rotate in an angle relative to a center of the rotor, where the poles are configured to interact with one or more teeth in a stator via an electromagnetic field;
the stator is configured to be fixed in a stationary position in the electrical machine, where a gap, such as an air gap, is provided between the teeth and the poles in a lateral direction; and
at least one magnetic flux intensifier is arranged relative to at least one of the poles and at least one of the teeth, where the magnetic flux intensifier is configured to concentrate the magnetic field lines between that pole and that tooth during rotation of the rotor.
Description of Related Art
Magnetic flux leakage in the air gap between a stator and a rotor is a general problem in generators and motors, in particular in generators for wind turbines.
Various configurations and shapes of poles in rotors and stators have been proposed and it is commonly known that using a non-magnetic material as an intermediate ring holding the permanent magnets.
Recently, a trapezoidal magnetic flux intensifier pole arrangement has been proposed in U.S. Pat. No. 6,879,075 B2. This patent discloses a permanent magnet synchronous machine with a circumferential-oriented rotor assembly with trapezoidal shaped permanent magnets arranged between inversed trapezoidal shaped iron pole pieces.
U.S. Pat. No. 7,545,067 B2 discloses a permanent magnet rotor for generator, where the rotor has a shaft and a cylindrical plastic cage. The permanent magnets are inserted into recesses in the plastic cage that are shaped as dovetailed retainers for fixing the trapezoidal shaped permanent magnets tightly in the dovetailed retainers.
International Patent Application Publication WO 2011/135056 A1 discloses a permanent magnetic generator designed for wind turbines. This application discloses a cylindrical shaped rotor with an alternating arrangement of magnetic steel pole pieces and permanent magnet assemblies, where the trapezoidal shaped pole spices and the assemblies extend in a direction parallel to the rotation center axis of the rotor. Each assembly comprises two rectangular shaped permanent magnets placed on either side of a triangular shaped wedge made of magnetic iron.
Although these embodiments provide improved magnetic coupling techniques in the prior art, they still use a substantial amount of precious magnetic material. This increases the production costs for such magnetic rotor-stator couplings.
U.S. Pat. No. 5,631,512 discloses a motor having cylindrical shaped rotor having alternating arrangement of air gaps, permanent magnets, and pole pieces made of a soft magnetic material. The pole pieces are placed on one side of the permanent magnets, while the air gaps are located on the other side of the permanent magnets separating it from an adjacent pole piece. The pole pieces are formed by an integrated part of the rotor body while the air gaps are formed by recesses in the body of the rotor. The permanent magnets and the pole pieces have the same arc length. The soft magnetic material is only arranged on the front side of the permanent magnets relative to the rotation direction of the rotor which means that magnetic flux at the backside will not be intensified, since the air gap acts as a non-magnetic material. Furthermore, this configuration still uses a lot of expensive magnetic material to form the rotor assembly.